Recently, the IC has a plurality of terminals formed on the side or the bottom of the main body thereof, and variety of IC sockets for lowering the inductance of the contact have been developed as the frequency of the operation signal becomes higher and higher. In order to improve the high frequency characteristics for the IC socket by means of realizing a low inductance like this, it is necessary that the length of the signal line of the socket contact should be as short as possible. On the other hand, the contact must be provided with a structure so as to compress and come in contact elastically with the lead portion of the IC. Because of the above, for example, for the contact of a type where a spring portion is prepared when the contact is punched off from a metal plate, shortening of the length of the spring i.e. shortening of the length of the signal line is restricted from the aspect of compressing-contact characteristic. Therefore, it is difficult to achieve lowering the inductance to a predetermined level by means of this type of contact.
To overcome the problem like the above, an IC socket with a structure, which has a resilient member of rubber elasticity interposed between the contact coming into contact with the lead portion of the IC and the socket cover above it, is shown in Japanese Patent No. 2849070, in order to keep the contact a standby posture and obtain a contact pressure between the contact and the IC lead by means of a restoring force of the resilient member.
However, because the number of IC leads increases as the IC becomes highly integrated or highly functionalized, it becomes hard to obtain a uniform contact pressure to the IC leads over the all contacts. Consequently, there has been a problem to ensure an appropriate compressing-contact condition between the IC lead and the socket due to occurrence of possibility of such as a partial non-contact between the contact and the IC. In view of the problem above, Japanese Patent No. 3822539 has disclosed an IC socket that assures an appropriate characteristic of the IC upon realizing a uniform contact pressure to the IC over the all contacts.
Nowadays, semiconductor devices constituting the IC (Integrated Circuit) are progressing in miniaturization of semiconductor elements, so that speeding-up of operation thereof and narrowing of the pitch of the lead terminals are going forward. To this end, packaging technology that does not damage the performance of electrical property of semiconductor devices such as high frequency characteristics, or characteristic estimation technology is increasingly being important. Because of the above, densification of IC packaging, and miniaturization and narrowing of the pitch of the lead pattern in a circuit board have been progressing. Besides, further downsizing of the IC socket that is a contact medium between the IC and the circuit board and lowering of the impedance including lowering of the inductance have been strongly required. Here, the IC socket is used for packaging of the IC to the circuit board, or for electrical test, burn-in test, etc. of the IC.
The present invention is carried out in view of the circumstances mentioned above and intended to provide an IC socket, which realizes a novel contact making easier lowering the height of the IC socket for downsizing and lowering the impedance than ever before and corresponds favorably to improvement of the high frequency characteristics and miniaturization of the IC.